Use of a medium as a seedbed for growing a plant, on which a seed of the plant is put and which is then transplanted in the ground, is effective in accelerating germination and preventing the plant from dying or being retarded in the initial stage of growth.
Such a medium for growing a plant includes known aqueous gel medium as disclosed in JP-A-63-71108 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
After a seed is planted on the known aqueous gel medium, the root grow through an aqueous gel, such as agar, while absorbing water of the gel.
However, since oxygen is supplied to the root growing deep in the aqueous gel only through diffusion from the gel surface into the inside of the gel, sufficient oxygen cannot be fed, and the growth of the plant is hindered. As a result, plants tend to die, or their initial growth tends to be extremely retarded.
Furthermore, cases often occur in which the root of the seed sown on aqueous gel medium .beta. cannot enter the gel but creeps down the outer wall of the gel as shown in FIG. 2(b) (hereinafter referred to as "creeping down of the root"). If it happens, the aqueous gel is not made use of, resulting in growth insufficiency and the like.
Even those plants that have escaped such direct hindrances as mentioned above tend to fail to receive sufficient supply from the gel after being transplanted in the ground when the weather turns to slightly dry, often resulting in growth retardation or death.
Because of these serious drawbacks and little effect, seldom has the known aqueous gel medium been applied to practice use in growing a plant.
In order to overcome the drawbacks associated with the known aqueous gel medium for growing a plant, an aqueous gel medium for growing a plant shown in FIG. 3 as .gamma. has been previously developed (hereinafter referred to as a "shelf-containing bored medium").
The shelf-containing bored medium .gamma. has hole 3 for letting a root grow therethrough as shown in FIG. 3(b) and hole 2 for seeding the diameter of which is slightly larger than the diameter of a seed to be put therein as can be seen from the cross section of FIG. 3(a-2). A seed put into the hole 2 is held there by shelf 4 formed by the difference in diameter between the holes 2 and 3.
Although the shelf-containing bored medium .gamma. solves the problems of the known aqueous gel medium having no hole, it necessitates preparing a variety of media different in diameter of the hole for seeding so as to cope with various kinds of plants. If a seed is put into a hole whose diameter is too large for the seed, the humidity of the atmosphere surrounding the seed would be insufficient for obtaining satisfactory results in terms of rate of germination or uniformity of the time of germination.
Accordingly, if seedlings of various kinds of plants are to be produced, as many shelf-containing bored media .gamma. different in the diameter of the hole for seeding as the kinds of the plants must be stocked, which entails cost and requires a space. A stock of aqueous gel media should be stored with care not to dry or to prevent generation of mould because of its aqueous character. Therefore, it is disadvantageous to keep the stock of aqueous gel media.